1. Field of the Invention
The present invention relates to a drive checking system for fan filter units in a clean room. More particularly, the malfunctioning of each of a plurality of fan filter units used for air conditioning in a semiconductor clean room is detected individually and produces an alarm, so that proper air conditioning in the clean room is maintained more efficiently.
2. Description of the Related Art
Generally, a clean room for manufacturing semiconductor devices has an air conditioning system to circulate and maintain the cleanliness of the air therein. There are two types of air conditioning systems used in clean rooms; a central system using a large circulation fan, and an individual system using a plurality of small fan filter units. As comparted to the central system, the individual system has the advantages of compact structure, little noise, little vibration, energy savings, and easy control of air flow. Therefore, the individual air conditioning system, employing multiple small fan filter units, is becoming more widely used in semiconductor clean rooms than the central air conditioning system using the large fan. The fans used in the air conditioning system in the normal semiconductor clean room are illustrated in U.S. Pat. No. 5,069,113.
In the individual air conditioning system, a plurality of fan filter units 10, one of which is shown in FIG. 1, are installed in the ceiling of a clean room according to a specified arrangement. The fan filter unit 10, which includes a filter 18 and air supply fan 12, filters the circulating air and supplies it to the clean room. Using the conventional fan filter unit 10, air is introduced from the ceiling of the clean room as driven by the fan 12. The air then flows along a flow path inside a housing 14, through an insulator 16, a grid plate at the filter interface, and then through the filter 18 before flowing into the clean room.
Inside the clean room the air flows downward from the ceiling to the bottom of the clean room, where it is collected in an air circulation duct which carries it again to the ceiling. The air is then recirculated by the fan filter unit. In this arrangement, particles are directed to the bottom of the clean room by the air stream, which prevents the particles from being introduced into the semiconductor device fabrication equipment on the production line. Also, the pressure in the clean room is maintained at a higher level than the pressure outside to prevent the particle-containing air outside the clean room from being introduced into the clean room.
Since the normal air conditioning system for a clean room has a plurality of fan filter units, as described above, it is difficult to monitor and detect a malfunction (i.e., an abnormal operational state) in each fan filter unit. Normally, the abnormal operational state of a fan filter unit is detected only by checking the state of the current or the voltage that is supplied to the fan. However, this method cannot detect a malfunctioning fan filter unit accurately and directly because sometimes the fan filter unit is malfunctioning even when the current or voltage is supplied correctly.
As a result, in the individual unit air conditioning system, an adverse air stream can be generated when a fan filter unit malfunctions causing contaminating particles to be introduced into the clean room. Further, the adverse air stream may continue undetected for a long time. The malfunction of several fan filter units out of the entire arrangement of fan filter units can have a serious adverse effect on the air environment inside the clean room and cause a decrease in the productivity of the fabrication facility.